Process for treating water with bromine



' 30 p.p.m. of bromine.

United States Patent of application Ser. No. 283,596, May 27, 1963. Thisapplication June 1, 1966, Ser. No. 537,246

Claims. (Cl. 210-62) This application is a continuation of Ser. No.283,596, filed May 27, 1963, now abandoned.

This invention relates to a process for treating an aqueous solutionwith bromine to control the microorganisms therein. More particularly,it relates to a process for treating water with elemental bromineobtained has been a standard practice in the United States and abroadfor many years. Addition of bromine in concentrations up to 5 parts permillion (p.p.m.) to sanitize water was described by Henderson in UnitedStates Patent 1,995,639. Now it is generally recognized that on anequimolar basis, bromine is several times more effective than chlorinefor the control of bacteria, algae, slime, and other microorganisms inwater supplies. In fact, excellent control of many bacteria in water canbe effected using as little as 0.1 p.p.m. bromine.

With badly contaminated water, a heavy initial shock sirable to kill thecontaminating microorganisms after which a residual bromineconcentration of 0.1 to 1.0 p.p.m. is generally elfective in maintainingsanitary water. level of the shock treatment is, of course, dependent onthe nature of the contaminating microorganisms. For treatment of potablewater, shock treatment with 3 to 5 ppm. bromine generally suifices tokill the undesired bacteria. However, heavy contamination with slime andalgae, as may be encountered in water used in industrial cooling towers,often requires shock treatment with to For example, while treatment with2 p.p.m. bromine noticeably inhibits the growth of Chlorella, a co'mmonstrain of algae, 10 p.p.m. bromine are required for pronouncedinhibition and between 10-20 p.p.m. for complete kill.

-In addition to its efiectiveness as an antimicrobial, there are furtheradvantages to the use of bromine in sanitizing water supplies Because ofits lower volatility, maintaining a desired residual level of halogen inthe treated water is easier with bromine than chlorine, particularlyunder conditions of turbulent how and agitation. Furthermore, bromineimparts little or no undesirable taste or odor to the treated water.Indeed, since bromine acts to destroy suspended or dissolved organicmatter which often causes undesirable color and odor, it is particularlysuited for use as a sanitizing agent for swimming pools where sparklingclear, colorless and odorless water is highly desirable.

Thus, treating water with bromine is advantageous in providinglarge'volumes of Water suitable as potable municipaly supplies and formany other commercial, industrial and residential purposes. Inparticular, bromine is extremely desirable for use as a sanitizing agentfor swimming pools, industrial cooling towers, and similar recirculatingwater systems since a very low concentration of bromine is effectiveboth in destroying the bacteria initially present and in maintaininghygienic conditions in spite of repeated recontamination.

Patented Apr. 25, 1967 its use as a sanitizing agent, particularly insmaller systems Where elaborate equipment for handling liquid bromine isnot feasible. In some localities use of liquid bromine has beenrestricted by ordinance.

Thus, there exists -a need for a safe and practical process wherebybromine can be stored, handled, and added to water by unskilledpersonnel. Such a process requires a form of bromine which is easily andsafely prepared, which is stable during storage and shipment, which doesnot cause serious burns in case of accidental skin contact, and yetwhich releases elemental bromine as required for sanitizing treatment.

It has now been discovered that the: polybromide form of strongly basic,quaternary ammonium anion exchange resins is an extremely convenient,effective, and safe means for handling elemental bromine for use intreating Water to control microorganisms. Essentially the polybromideresin serves as a reservoir from which elemental bromine can be removedas required to establish or to maintain control of bacteria, algae,slime, and other microorganisms in a body of water. Not only do suchpolybromide resins possess highly useful and desired properties inrespect to both bromine loading and elution charactertions and can beprepared, stored, out degradation in quality. Although definitely notrecommended, momentary accidental contact of the polybromide resin evenwith wet skin will not cause burns. Furthermore, the aqueous solutionobtained by contact of the polybromide resin with water is sufiicientlydilute so that burns will not result from brief skin contact.

Thus, the invention described herein concerns an improved process fortreating water with bromine. More particularly, this improved processcomprises: (1) contacting an anion exchange resin in polybromide formwith water whereby bromine is removed from the polybromide resin to givean aqueous solution containing from 10 to 10,000 p.p.m. bromine and (2)mixing a sufiicient amount of said aqueous bromine solution with thewater to be treated to establish therein a concentration in the rangefrom about 0.02 to 30.0 p.p.m. bromine.

The adsorption of elemental bromine by an anion exchange resin wasreported in Chem. and Ind, 1238 (1957) by Aveston and Everest who foundthat when an anion exchange resin was treated with an aqueous solutioncontaining elemental bromine, the polybromide anion, Br wherein n is 3,5 or 7, became the predominant anionic species in the resin phase. Witha quaternary ammonium resin and excess bromine, the resin was convertedto the BI'7 form by adsorption of 3 moles of bromie per equivalent ofresin.

Ziegler in Angew. Chemie, 71, 283 that the polybromide resin was stablefor a period at least 1.5 years. Furthermore, Ziegler found that thebromine was quantitatively eluted from the resin as bromide ion bytreatment of the polybromide resin with an aqueous solution of areducing agent, such as sulfur dioxide or sodium bisulfite. However,elution of bromine from the polybromide resin as an aqueous solutioncontaining from 10 to 10,000 p.p.m. of elemental bromine as describedherein has not been previously reported.

In the practice of the present invention, commercial anion exchangeresins prepared by the reaction of a chlorornethylatedstyrene-divinylbenzene resin with an appropriate organic amine aresuitable as; bromine carriers. Strongly basic, quaternary ammonium anionexchange resins of the type described by McBurney in (1959) reportednited States Patent 2,591,573 and by Bauman and Mclellar in UnitedStates Patent 2,614,099 are particularly esirable. Weakly basicpolyamine anion exchange resin, uch as described by McBurney in UnitedStates Patent ,591,574, may also be employed although the polyhalide ormof these resins is not as stable.

Since the operating characteristics of the polybromide mion exchangeresin column are similar to those of conentional ion exchange resincolumns, commercial resins ind conventional operating techniques aregenerally satisfactory in terms of such factors as degree of resincrossinking, mesh size, flow rates, etc. While commercial inion exchangeresins are commonly available in the :hloride form, any anionic form maybe employed so long as the anionic component is exchangeable by bromideor polybromide ions. Hydrolysis of bromine in the aqueous solution usedto prepare the polybromide resin is generally sufficient to convert theresin to the desired bromide form. However, conversion from one anionicform to another is readily accomplished by wellknown ion exchangetechniques if necessary.

A particularly effective method for the preparation of a suitablepolybromide resin is to pass an essentially saturated solution ofbromine in aqueous sodium bromide slowly up through a bed of quaternaryammonium anion exchange resin. In this manner a commercial resin havinga dry weight capacity of 3.50 meq./g., Cl"- form, rapidly adsorbed 3moles of bromine per equivalent of quaternary ammonium groups. Theresulting polybromide resin in wet form contained about 48.6 weight percent bromine. This adsorbed bromine was quantitatively removed bytreatment with a sodium bisulfite solution. An attempt to load the resinfurther under more forcing conditions resulted in 'bromination of theresin matrix, the elutable bromine content remaining at about 3 molesper equivalent of resin. A cubic foot of wet quaternary ammonium resinin the B17 form contains about 40 pounds of bromine, an amountsufficient to treat a 25,000 gal. swimming pool for a normal period ofat least 30 days.

If the polybromide resin is dried or exposed to large volumes of air,some of the adsorbed bromine is lost. However, if stored in a sealedcontainer of bromine-resistant material such as polyvinyl chloride, theresin is stable for prolonged periods.

With conventional flow rates of from 1 to g.p.m./ ft. of resin bedcross-sectional area, elution of bromine from the polybromide resin bypassing water through the resin bed is essentially independent of theexact method of contact. An equilibrium is rapidly established betweenthe bromine adsorbed by the anion exchange resin and that present in theaqueous phase. At room temperature the aqueous phase in contact with aquaternary ammonium resin in a fully loaded 'Br'r form contained about7,000 p.p.m. bromine. Elution studies with a column of this resinindicated that the bromine concentration in the eluent dropped to about1,300 p.p.m. after 100 bed volumes of water passed through the column.After passage of 1,400 bed volumes, the bromine concentration in theeluent dropped to about 50 p.p.m. and about 95 percent of the adsorbedbromine had been removed. Further elution reduced the residual brominecontent of the resin still lower and the eluent bromine concentrationthen dropped to 10 p.p.m. and less.

Temperature does have a .marked effect on the equilibrium of brominebetween the resin and aqueous phases. For example, water in contact withan approximately equivalent amount of polybromide resin containing 2.14moles of bromine per equivalent of resin had an equilibriumconcentration of about 13,800 p.p.m. bromine at 55 C. and 4,270 p.p.m.at 27 C.

Regeneration of the exhausted or partially exhausted polybromide resinis readily achieved by treatment with a more concentrated brominesolution whenever desired, generally when the concentration of brominein the eluent falls below a given level. Yet obviously a higher eluentconcentration of bromine is needed for a shock treatment requiring 10-30p.p.m. bromine in the treated water than for maintaining a residual of002-10 p.p.m. bromine. Hence, the frequency of regeneration will dependon the requirements of the particular system.

The bromine-containing eluent solution can be metered and added toanother body of water as required to establish or to maintain a desiredbromine concentration in the treated water. Conventional analyticaltechniques can be employed to determine bromine concentrations and tocontrol the treatment process. If desired, automatic equipment can beused to monitor continually the bromine concentration in the treatedwater and to add the more concentrated bromine el-uate as required tomaintain the bromine concentration within desired limits. Such controlis particularly suitable with a recirculating system such as commonlyemployedin residential swimming pools where a portion of the watercirculating through the system can be diverted by suitable means to passthrough and to elute bromine from a polybromide resin column.

The following examples illustrate further the invention described hereinbut are not to be construed as limiting its scope.

Example 1.-P0lybr0mide resins A. A portion of 20/50 mesh commercialquaternary am monium styrene-divinylbenzene anion exchange resin havinga dry weight capacity of 3.5 -meq./ g. Cl form (Dowex 1-X8 resin) wasplaced in a 1'' ID. glass column and loaded with bromine by slowlypassing an excess of an aqueous solution containing about 35 wt. percentbromine and 17 wt. percent sodium bromide up through the column. Aftercomplete loading, the excess bromine solution was drained from thecolumn and the polybromide resin rinsed with a small amount of water. Asample of the resulting wet polybromide resin was found to contain 48.6wt. percent bromine. The adsorbed bromine was quantitatively removed bytreatment of the resin with a sodium sulfite solution and correspondedto a theoretical capacity of 3 moles of bromine/ equivalent of resinanion exchange capacity.

B. In an attempt to load the resin further, the concentrated aqueousbromine solution was warmed to 50C. and recycled through the resin bedfor several hours. The resin was then allowed to stand at roomtemperature for several days in contact with the bromine solution. Theresulting wet resin was found to contain 64.9 wt. percent total bromine.However, after treating this resin with excess sodium sulfite solution,it retained 16.4 wt. percent bromine indicating bromination of the resinmatrix. The elutable bromine was equivalent to about 3 moles of bromineper equivalent of initial resin capacity.

C. In a similar manner the polybromide forms of otherstyrene-divinylbenzene resin containing from 1 to 16% divinylbenzenewere prepared. Also, a quaternary poly- (vinylpyridine) resin asdescribed by Greer in United States Patent 2,801,223 and a commercialquaternized polyethoxypolyamine resin were converted to similarpolybromide forms. Although the bromine capacities of these resins weresimilar in proportion to their initial anion exchange capacity, thelatter two resins were less stable than the preferred quaternaryammonium styrene-divinylbenzene resins.

Example 2.-Eluti0n characteristics Using a 1 ID. column filled with thepolybromide form of Dowex l-XS resin prepared as described in Example1A, a series of elution runs was made at room temperature. Noappreciable variation in elution characteristics was found using flowrates of 5 and 10 g.p.m./ft. a bed depth of 18 and 36 inches, and upflowand downfiow feed. Table I presents data from a typical elution runusing a wet resin containing initially 48.5 wt. percent bromine.

TABLE I.--ELUTION CHARACTERISTICS Example 3.-Swimming pool unit A smallresin column, 4" in diameter and 18" high, loaded with 0.13 ft. of Dowex1-X8 resin in the polybrornide form and containing about 5.2 lbs. ofbromine, was installed in the recycle line of a 20,000 gallon outdoorresidential pool. By means of appropriate valves, a portion of therecycle water could be diverted after the filter unit to pass throughthe resin column, thereby eluting a portion of the adsorbed bromine foraddition to the main recycle stream.

Initially flow of recycle water through the resin column Was controlledmanually to maintain a bromine concentration in the main body of thepool between about 0.70 and 1.20 ppm. Subsequently an automaticinstrument was installed to measure the residual bromine in the recyclestream and to control a solenoid valve on the line to the polybromidecolumn thereby diverting a portion of the recycle stream through thepolybromide resin column intermittently as required to maintain adesired lbromine concentration. For example, in a warm mid-afternoonperiod, the resin column was used with a cycle of about minuteson-stream followed by about minutes oil-stream. After each on-streamperiod, the bromine concentration in the pool continued to rise for afew minutes because of the pool mixing characteristics before droppingslowly as the bromine was consumed. N onetheless the bromineconcentration in the pool was easily maintained between about 0.80 to1.05 ppm. During the night, bromine consumption Was essentially nil.

During an extended test period with the polybromide resin column, theswimming pool showed no signs of algae growth and maintained anessentially sterile condition with a bacterial plate count of less than0.1 per cc.

We claim:

1. In a process for treating an aqueous solution with bromine, theimprovement which comprises:

passing the aqueous solution through a bed of a water- 6 insoluble anionexchange resin in poly-bromide form,- whereby bromine is removed fromthe polybromide resin by the aqueous solution.

2. In a process for treating an aqueous solution with bromine to controlthe microorganisms therein, the improvement which comprises:

(1) contacting a water-insoluble anion exchange resin in polybromideform with an aqueous solution whereby bromine is removed from thepolybromide resin to give an aqueous solution containing from 10' to10,000 ppm. bromine and (2) mixing a sufiicient amount of said brominesolution with the aqueous solution to be treated to establish therein aconcentration in the range from about 0.02 to 30.0 ppm. bromine.

3. The process of claim 2 wherein a portion of the aqueous solution tobe treated is used to remove bromine from the polybromide resin.

4. The process of claim 2 wherein the water-insoluble anion exchangeresin is a quaternary ammonium anion exchange resin.

5. The process of claim 4 wherein the predominate anionic species in theresin phase prior to initial elution is the polybromide anion, BT11,wherein n is an odd integer from 3 to 7 inclusive.

' References Cited by the Examiner UNITED STATES PATENTS 3,037,8456/1962 Hein 23-154 3,075,830 1/1963 Schoenbeck 23-216 3,098,716 7/1963Gradishar et al 23-217 3,101,250 8/1963 Schoenbeck 23-87 3,116,9761/1964 Gradishar et a1 23-216 3,140,976 7/1964 Berenschot et a1 210-643,152,073 10/1964 Morton 210-62 References Cited by the Applicant UNITEDSTATES PATENTS 3,174,828 3/1965 Hein.

FOREIGN PATENTS 1,013,391 12/1965 Great Britain.

MORRIS O. WOLK, Primary Examiner. E. G. WHITBY, Assistant Examiner.

1. IN A PROCESS FOR TREATING AN AQUEOUS SOLUTION WITH BROMINE, THEIMPROVEMENT WHICH COMPRISES: PASSING THE AQUEOUS SOLUTION THROUGH A BEDOF A WATERINSOLUBLE ANION EXCHANGE RESIN IN POLYBROMIDE FORM, WHEREBYBROMINE IS REMOVED FROM THE POLYBROMIDE RESIN BY THE AQUEOUS SOLUTION.